test: Clean up trajectories

[ValerianRey]

The idea behind this is to keep the trajectories package clean, with only the experiments that we pushed enough to put them in the paper.

Summary

• Rename QuadraticForm → QuadraticFunction (and subclasses) — these are not quadratic forms in the linear-algebra sense
• Remove the CQF, MN2, and MN20 objective configurations and all their associated constants
• Remove the nashmtl20 aggregator and its constants
• Rename CQF2 → CQF
• Add a usage example to run all trajectories of the paper at once

🤖 Generated with Claude Code

[PierreQuinton]

I do not have much expertise on this part of the repo, I think it is fine if it runs correctly.